1. Field of the Invention
The present invention relates to a longitudinal locking mechanism for use in a vehicle seat. The longitudinal locking mechanism has a rod slidably inserted in a cylindrical body along the longitudinal direction thereof such as to permit the rod to be adjustably locked in a selected length for adjustment of a movable element in the vehicle seat.
2. Description of Prior Art
As widely known in a seat for vehicles, a longitudinal locking mechanism is employed as one of mechanical lock devices to lock and unlock a movable element in the seat such as a reclining device or seat height adjuster. Hitherto, most of such longitudinal locking mechanism has been of the construction wherein a rod is slidably accommodated in a cylindrical body in the longitudinal direction thereof, with a torsion spring being wound around the rod. According to this conventional locking mechanism, the rod is throttled strongly by the torsion spring and retained in a locked state due to a friction therebetween, thereby projecting its free end portion in a selected length from the cylindrical body. The rod may be released from the locked state by forcibly reducing the throttling force of torsion spring and permitted to be projected from and withdrawn into the cylindrical body as desired. In that way, the free end portion of the rod may be adjusted in length for applications to adjustments of movable elements in the seat.
The locking strength in this conventional torsion spring locking mechanism is dependent only upon a frictional force between the rod and torsion spring. It has been found that errors in diameter between the torsion spring and rod, or variation of spring force in each torsion spring, which are apt to occur during assemblage, will inevitably result in undesired variations of frictional force between the rod and torsion spring in each of the locking mechanisms and therefore there will be no constant quality and no reliability of locking performances in this sort of conventional longitudinal locking mechanism. In other words, assembling such torsion-spring longitudinal locking mechanism requires a high precision in maintaining a constant quality of the torsion spring and rod in terms of their relative dimensions and requires a high expertise in assembling them together, with the result that a more intricate design of structure or troublesome labor is inevitably demanded on the part of workers, which incurs much costs involved. Moreover, normally, the unlocking operation in this mechanism requires a cocentric rotary action about the torsion spring to reduce the throttling force of the same spring to the rod, and such rotary action is made in a directin transversing the width-wise direction of seat, giving uneasy and hard fealing to a user as compared with a longitudinal drawing or pressing action.